Series-capacitor compensation equipment

Abstract

This series-capacitor compensation equipment comprises a series-capacitor bank in series with a power line and an overvoltage protection circuit for the capacitor bank comprising the series combination of a surge arrester and electric bus structure connected in series with the power line and in parallel with the capacitor bank. The surge arrester includes metal-oxide varistor elements which impart a relatively high resistance to the arrester when the voltage across the arrester is in a normal range and a relatively low resistance when the voltage across the arrester rises to a predetermined value that produces arrester operation. The capacitor bank will discharge through the overvoltage protective circuit should a varistor element fail during arrester operation. The bus structure comprises stainless-steel bus conductor having a resistance that is sufficiently high to effectively limit the energy duty on the arrester during discharge of the capacitor bank through the overvoltage protection circuit in the event of failure of a varistor element during arrester operation.

What we claim is: 
     
       1. Series-capacitor compensation equipment comprising: (a) a series-capacitor bank for connection in series with a power line,   (b) an overvoltage protection circuit for the series-capacitor bank for connection in series with said power line and in parallel with said series-capacitor bank, the overvoltage protection circuit comprising the series combination of a surge arrester and bus structure, the surge arrester comprising an insulating housing and varistor elements within said housing, said bus structure being located externally of said housing and connected in series with said varistor elements, and in which:   (c) said bus structure comprises stainless-steel bus conductor having a resistance that is sufficiently high to effectively limit the energy duty on the surge arrester during discharge of said series-capacitor bank through said overvoltage protection circuit in the event of a failure of a varistor element during surge-arrester operation.   
     
     
       2. The series capacitor compensation equipment of claim 1 in which the resistance of said stainless-steel bus conductor is sufficiently high to prevent rupture of said insulating housing as a result of discharge of said series-capacitor bank through said overvoltage protection circuit in the event of a failure of a varistor element during surge-arrester operation. 
     
     
       3. The series-capacitor compensation equipment of claim 1 in which the resistance of said stainless steel bus conductor is sufficiently high as to limit the peak amplitude of the capacitor-discharge current to a value substantially lower than that which would flow under corresponding capacitor discharge conditions in an otherwise corresponding series-capacitor compensating equipment in which the surge arrester is connected into the power circuit by bus structure made substantially entirely of aluminum bus conductor of much larger cross-section than the stainless-steel bus conductor. 
     
     
       4. The series-capacitor compensation equipment of claim 1 in which said stainless-steel bus conductor has a relatively small transverse cross-section as compared to that of the aluminum bus conductor present in an otherwise corresponding series-capacitor compensation equipment in which the surge arrester is connected into the power circuit by bus structure made substantially entirely of aluminum bus conductor and large enough in transverse cross-section to avoid overheating should the capacitor bank discharge therethrough as a result of a varistor element failure during a fault on said power line. 
     
     
       5. The equipment of claim 4 in which the transverse cross-section of said stainless-steel bus conductor is sufficiently small as to provide an increased inductance that substantially reduces the frequency of the capacitor-discharge current as compared to the frequency of the capacitor-discharge current that flows under corresponding capacitor-discharge conditions in said otherwise corresponding equipment. 
     
     
       6. The series-capacitor compensation equipment of claim 1 in which said stainless-steel bus is several tens of feet in length. 
     
     
       7. The series-capacitor compensation equipment of claim 1 in which said stainless-steel bus conductor is made of a stainless steel capable of continuous operation without damage in an uncontrolled atmosphere at temperatures up to 800° C. 
     
     
       8. The series-capacitor compensation equipment of claim 1 in which said stainless-steel bus conductor is of a stainless steel consisting essentially of, by weight, about 18% chromium, about 8% nickel, and about 74% iron. 
     
     
       9. The series-capacitor compensation equipment of claim 1 in which said stainless-steel bus conductor includes a plurality of series-connected lengths interconnected by bends that allow said lengths to bend in response to thermal expansion of the lengths when heated by high currents therethrough. 
     
     
       10. The series-capacitor compensation equipment of claim 1 in which said bus conductor structure further comprises additional bus conductor electrically connected in series with said stainless-steel bus conductor, said additional bus conductor being made of at least one of aluminum, copper, or alloys thereof.